Tellurium compounds hexafluoride

Sihcon and boron bum ia fluorine forming siUcon tetrafluoride [7783-61-17, SiF, and boron trifluoride [7637-07-2] respectively. Selenium and tellurium form hexafluorides, whereas phosphoms forms tri- or pentafluorides. Fluorine reacts with the other halogens to form eight interhalogen compounds (see Fluorine compounds, inorganic-halogens). 

Elemental tellurium and the stable tellurides of heavy nonferrous metals are relatively inert and do not represent a significant health hazard (43—47). Other, more reactive tellurides, including soluble and volatile tellurium compounds such as hydrogen telluride [7783-09-7] > tellurium hexafluoride [7783-80-4], and alkyl tellurides, should be handled with caution. Some of these materials can enter the body by absorption through the skin or by inhalation and ingestion of dust or fumes. No serious consequences or deaths have been reported in workers exposed to tellurium and its compounds in industry (48). 

Note The REL and PEL also apply to other tellurium compounds (as Te) except Tellurium hexafluoride and Bismuth tellurlde.] ... 

Tellurium(VI)-nitrogen bonds can be generated by the reaction of hexamethyldisilazane with tellurium hexafluoride (Eq. 2.12). The product (Mc3SiNH)TeE5 is a useful precursor for a variety of NTeEs compounds. By contrast, SEe is inert towards Si-N reagents. 

The threshold limit value (TLV) set by the American Conference of Industrial Hygienists (ACGIH) for tellurium and its compounds is 0.1 mg/m3 which is about ten times the amount which has been known to produce the adverse garlic odor (45,50). The ACGIH TLV for tellurium hexafluoride is 0.1 mg/m3 or 0.02 ppm of air. Likewise, the U.S. Occupational Safety and Health Administration (OSHA) has established its permissible exposure limit (PEL) for tellurium and its compounds at 0.1 mg/m3 the PEL for tellurium hexafluoride is 0.2 mg/m3 or 0.02 ppm of air (50). 

Tellurium Halides. Tellurium forms the dihalides TeCl and TeBi, but not Tel2. However, it forms tetrahalides with all four halogens. Tellurium decafluoride [53214-07-6] and hexafluoride can also be prepared. No monohalide, Te2X2, is believed to exist. Tellurium does not form well-defined oxyhalides as do sulfur and selenium. The tellurium halides show varying tendencies to form complexes and addition compounds with nitrogen compounds such as ammonia, pyridine, simple and substituted thioureas and anilines, and ethylenediamine, as well as sulfur trioxide and the chlorides of other elements. 

Tellurium hexafluoride itself has been found to form complexes with potassium, rubidium and cesium fluorides. The cesium compound has a stochiometry approaching Cs2TeF8 and, in these types of complexes, the stability of the lattice appears to be inversely related to the polarizing power of the cation and the compounds are only stable in the solid state.41 Several heptafluorotellurates(VI) have been prepared from the reaction of tellurium with chlorine trifluoride in anhydrous hydrofluoric acid followed by addition of the metal fluoride.42... 

Tellurium hexafluoride heated with at least 4.5 molar equivalents of a primary alcohol at 90° for 9 days in the presence of excess sodium fluoride, formed a mixture of alkoxy tellurium fluorides containing cis- and trans-tetraalkoxy tellurium difluorides1. These mixtures could not be separated by distillation. The compounds were identified by 19F-NMR spectroscopy. 

Trifluoroethanol had not formed any tetraalkoxy tellurium difluoride after 9 days. After 28 days the mixture contained 29% of this compound. In reactions with prop-2-en-l-ol, decomposition occurred after five days. The reaction between tellurium hexafluoride and n-propanol produced no tetrapropoxy tellurium difluoride1. 

Equimolar amounts (0.1 mol) of tellurium hexafluoride and bis[trimethylsilyl]amine formed explosive cis-bis[trimethylsilylamino] tellurium tetrafluoride when heated at 60° in a steel cylinder3. The compound is a colorless crystalline material that can be sublimed at 40°/0.001 torr. 

All of these compounds are stable gases, exhibiting the maximum valency of the elements. They neither attack glass nor decompose spontaneously. The selenium and tellurium fluorides attack mercury making it adhere to glass, and m this respect they resemble (worn. Sulphur hexafluoride does not do this. 

Pentaalkoxy tellurium monofluorides were formed by fluorination of tetramethoxy telluriums by reaction of cw-tetramethoxy tellurium difluoride with sodium methoxide in methanolS by the action of anhydrous hydrogen fluoride on hexamethoxy tellurium, and by the condensation of primary alcohols with tellurium hexafluorideS None of these compounds was isolated. Their presence in the reaction mixture was detected by F-NMR spectroscopy. 

Sulphur, selenium and tellurium all form the hexafluoride by direct combination other hexahalides are unknown. SFg and SeFg are chemically inert, colourless gases. The former is non-toxic and at once the most inert sulphur compound and possibly the most inert non-ionic fluorine compound it resists fused KOH. The somewhat more reactive SeF is reduced by NHg above 200"". TeFg, also a colourless gas, is hydrolysed by water ... 

The heavier elements of the group, S, Se and Te all form tetralluorides, EF4 and hexafluorides, EF6- If the central atom in these compounds form Lewis electron pair bonds to all the ligating fluorine atoms, it must accommodate five or six electron pairs in the valence shell, and we refer to the atoms as hypervalent. Sulfur forms no further homoleptic hypervalent derivatives. Selenium forms a solid tetrachloride, but as mentioned in the last paragraph, it decomposes on evaporation. Tellurium forms a solid tetrachloride, which may be evaporated without decomposition, as well as tetraphenyl-, tetramethyl- and hexamethyl- derivatives. 

Oxygen forms the compound OF2, but sulfur, selenium, and tellurium form the hexafluorides, XFg. Comment on this situation. What is the hybridization of the central atom in these compounds ... 

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